SLNG plugin for LiveKit Agents

Support for SLNG's voice AI gateway in LiveKit Agents, providing access to multiple STT and TTS providers through a unified API.

See https://docs.slng.ai/ for more information.

Installation

pip install livekit-plugins-slng

Pre-requisites

You'll need an API key from SLNG. It can be set as an environment variable: SLNG_API_KEY

Usage

Pass an SLNG model identifier; the plugin connects through SLNG's Unmute Bridge and builds the endpoint itself.

from livekit.plugins import slng

stt = slng.STT(
    model="deepgram/nova:3",
    language="en",
)

tts = slng.TTS(
    model="deepgram/aura:2",
    voice="aura-2-thalia-en",  # provider voice ID, required
    language="en",
)

Additional keyword arguments are forwarded to the gateway and applied according to the selected model's contract. Failover across multiple models or endpoints is available via connections=[...]; see docs.slng.ai for details.

End of turn finalization

For the lowest STT turn latency, let the plugin know when the user stops speaking. The plugin then sends a finalize signal so the provider returns the final transcript immediately instead of waiting for its own endpointing:

session = AgentSession(stt=stt, ...)
stt.attach_to_session(session)

Or wire it manually:

@session.on("user_state_changed")
def _on_user_state_changed(ev):
    stt.notify_user_state(ev.new_state)

Without this hook the plugin still works, but end of turn detection relies entirely on the provider's endpointing, which typically adds a few hundred milliseconds per turn.

Region override

The plugin supports gateway region routing via the region_override option on both STT and TTS. This maps directly to the gateway's X-Region-Override header. See the available regions at docs.slng.ai/region-override.

You can pass either a single region:

stt = slng.STT(
    api_key="your-slng-api-key",
    model="deepgram/nova:3",
    region_override="eu-west-1",
)

Or multiple preferred regions in priority order:

tts = slng.TTS(
    api_key="your-slng-api-key",
    model="deepgram/aura:2",
    voice="aura-2-thalia-en",
    region_override=["eu-west-1", "us-east-1"],
)

To constrain routing to a broad geographic zone instead of a specific region, use world_part_override (for example "eu"), which maps to the gateway's X-World-Part-Override header. region_override takes precedence when both are set.

Migrating from 1.x

Version 2.0 is a breaking change:

• All traffic goes through the Unmute Bridge. model_endpoint and model_endpoints were removed; pass a model identifier or connections=[...] instead.
• STT no longer defaults to model="deepgram/nova:3"; pass a model (or connections) explicitly.
• TTS voice is required and passed verbatim as the provider's voice identifier.
• Language codes are no longer normalized client-side; send the value the model expects (for example BCP-47 hi-IN for Sarvam, not hi).
• STT recognize() (HTTP batch) is no longer supported; use stream(). Only pcm_s16le input audio is supported.
• api_token still works on STT but is deprecated; use api_key.